They were exposed to fire, but according to the rules of warfare set by the (Geneva?) convention, medics are not supposed to be shot at and killed (I believe this is still acknowledged today). Hence why they started painting big white patches with the red cross (the universal symbol for medic) all over them so the enemy would know they're a medic. Of course they got shot at anyways (and I mean shot at deliberately

. But by that code of conduct or whatever you want to call it, medics on both sides are supposed to not be targetted by enemy gun fire.
There's also an interesting scene in SPR where when the wall crumbles down and there's the standoff between the US guys and the Germans behind the wall. Ted Danson's character comes up and they shoot all the Germans. If you look, there's a brief scene where Wade (the medic) comes up and starts trying to help the just shot Germans. I'm not sure if this was also some kind of 'rules of warefare' thing where medics have to give medical attention to anybody they can type of thing (which is the code of a doctor anyways), or if it was just part of his character.
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Latuh fuh U,
Benson
benson@2015.com
"We don't introduce or cause bugs in the game, we merely find and bring to light the inadequacies within the code."
-regarding level designers